Matric Part 1/9th Class Physics Chapter 6 Long Question With Answer for Unit 6 Work and Energy

Question # 1

Q no:7 (B) Define Kinetic energy. Derive its formula K.E =1/2 mv²

Ans 1: Kinetic Energy :
The energy possessed by a body due to its motion is called kinetic energy.
Derivation:
Let a body of mass m is moving with velocity V. An opposing force F actingthrough a distance S brings it to rest. The body possesses kinetic energy and is capable to do work against opposing force F until all of its kinetic energy used up.
K.E of the body = Work done by it due to motion
K.E - FS
Vi = V
Vf =0
F = ma
a =-f/m
Since motion is opposed, hence , a is negative. Using 3rd equation of motion
2as =Vf² - Vi²
2 (-F/m)S =0² - V²
FS = +1/2 mv²
As we know that K.F is equal to the work done.
K.E =1/2 mv² ( proved )

Question # 2

What is meant by renewable sources of energy?

Ans 1: Renewable source of energy: the source of energy which wil not run out and can be used again and again are called renewable sources of energy
Example:
- Energy from water
- solar energy
- wind energy
- geothermal energy
- energy from biomass
Ans 2: Energy from water: water is a big source of production of energy in the form of electricity.
Energy from water power is very cheap. Dams are being constructed at suitable locations in different parts of the world. In dams, such stored water possesses potential energy due to its height. When this water stored at a height is allowed to fall down it is used to run power plants. These power plants convert the P.E of stored water into electricity. This electricity is then supplied thorough electric wires in the country.
Ans 3: Solar energy: solar energy is the energy coming from the sun.
Importance of solar energy:
- Solar energy can be used directly and indirectly
- Sunlight does not pollute the environment
- The sunrays are the ultimate source of life on the earth
- We are dependent on the sun for all our food and fuels
Ans 4: Wind energy: moving air is called a wind and energy possessed by the wind is called wind energy
Uses of wind energy: wind has been used as a source of energy for centuries
- It has powered sailing ships across the oceans
- It has been used by windmills to grind grain and pump water
- More recently, wind power is used to turn wind turbines
Ans 5: Geothermal energy: in some parts of the world, the earth provides us hot water rom geysers and hot springs. There is hot molten part, deep in the earth , called magma. Water reaching close to the magma changes to steam due to the high temperature of magma. This energy is called geothermal energy.
Conversion of geothermal energy into useful fuels: geothermal well can be built by drilling deep near hot rocks places, where magma is not very deep. Water is then pushed down into the well. The rocks quickly heat the water and change it into steam. This steam expands and moves up to the surfaces of earth. The steam can be pipe directly into house and offices for heating purposes or it can be used to generate electricity.
Biomass: biomass is plant or animal wastes that can be burnt as fuel. Other forms of biomass are garbage, farm wastes , sugarcane and other plants.
Energy from biomass: there are different ways tot get energy from biomass. Some of these are as follow
- Different forms of biomass are used to run power plants
- Many industries that use forest products get half of their electricity by burning bark and other wood wastes.

Question # 3

Write a note on energy a nd environment

Ans 1: Sources; environmental problems such as pollution that consist of noise , air pollution and water pollution may arise by using different sources of energy such as:
- Fossil fuels
- Nuclear energy
Ans 2: Pollution: polliton is the change in quality of environment that can be harmful and unpleasent for living things.
Thermal pollution: a temperature rise into the environment that disturbs life is called thermal pollution.
Effects:
- Thermal pollution upsets the balance of life.
- It endangers the survival of many species
Ans 3: Air pollutants: Air pollutants are unwanted and harmful. Natural processes such as volcanic eruptions, forest fires and dust storm add pollutant to the air. These pollutants rarely build up to harmful levels. On the other hand the burning fuel and solid wastes in homes, automobiles' and factories release harmful amount of air pollutants
Ans 4: Pollution from fission plans: al power plants produce waste heat, but fission plants produce the most. The heat released into a lake , a river , or an oven upsets the balance of life in them. Unlike other power plants , nuclear power plants don't produce carbon dioxide. But they do produce dangerous radioactive wastes.
Ans 5: Laws; in many countries government have passed laws to control air pollution. Some of these limit the amount of pollution that power plants , factories ad automobiles are allowed to give off. To meet this condition for automobiles , new cars have catalytic converts. These devices convert some polluting gases. The use of lead free petrol has greatly reduced the amount of lead in the air. Engineers are working to improve new kinds of car engines that use electricity or energy sources other than diesel and petrol. Many individual communities have laws which protect their areas from pollution. Individuals can help to control arir pollution simply y reducing the use of card and other machines that burn fuel. Sharing rides and using public transportation ar the way to reduce the number of automobile's in use.

Question # 4

What are nuclear fuels? explain it

Ans 1: nuclear fuels: the materials through which we can obtain nuclear energy are called nuclear fuels e.eg uranium element. In nuclear power plants wee get energy as a result of fission reactions.
Ans 2: Nuclear fission reaction: the process in which heavy nucleus breaks into two smaller nuclei releasing a loti of energy is called nuclear fission reaction. During fission reaction, heavy atoms splits into two smaller parts releasing large amount of energy.
Ans 3: Example: fission reaction of uranium element
Ans 4: Uses: nuclear power plants give out a lot of nuclear radiations and a vast amount of heat. A part of this heat is used to run power plants while a lot of heat goes waste into environment

Question # 5

What are fossil fuels? explain

Ans 1: Fossil fuels: natural fuel such as coal, oil and gas are called fossil fuels because they are produced by dead bodies of lining things.
Uses; we use fossil fuels such as coal, gas to heat our houses and run industry. They are usually hydrocarbons.
Ans 2: Hydrocarbons: hydrocarbons means compound of carbon and hydrogen. When they burnt they combine with oxygen from the air.
Ans 3: Non renewable sources: fossil fuels took million of years for their formation they are known as non renewable resources. We are using fossil fuels at very fast ratee. Their use is increasing day by day . If we continue to use them. They will soon exhausted. Once their supply is exhausted world would face serious problems. Therefore, we should use them wisely at same time develop new sources for future survival
Ans 4: Harmful waste : moreover fossil fuels release harmful waste as carbon monoxide and other harmful gases which pollute environment
Ans 5: Diseases: This may cause serious health problems such as headache, tension, nausea, allergy, irritation of eyes, nose , throat and may cause lungs cancer, asthma, heart diseases, damage of brain, nerves and other organs of our body.

Question # 6

Explain the mass-energy equation

Ans 1: Einstein predicted the interconversion of matter and energy. According to him, a loss in the mass of a body provides a lot of energy. This happen in the nuclear reaction. The relation between mass m and energy E is given by Einstein's mas-energy equation
E=mc²
Where c is the speed of light( 3*10⁸ ms^-1)
Ans 2: Significance; the above equation shows that tremendous amount of energy can be obtained from sample quaintly of matter. It happens that matter is highly concentrated form of energy
Ans 3: Uses: the process of getting the energy from our nuclear power plants is based on the above equation. The process is taking place on the sun and stars for the last millions of yeas. Only a very small fraction of the suns energy reaches the earth. This very small fraction of the suns energy is responsible for life on the earth.

Question # 7

What is energy converter ?

Ans 1: Energy converter : an energy converter is a device in which a part of energy taken by the system is converted into useful work. Remaining energy is dissipated as heat energy, sound energy, noise into the environment
Ans 2: Important energy converters: here are some most important energy converters
1. Electric lamp
2. Energy saver lamp
3. Vehicle running with constant speed on a level road
4. power station

Question # 8

How is energy converted from one form to another? Give some examples

Ans 1: Interconversion of energy: the conversion of one form of energy into another form is called interconversion of energy.
Explanation: energy cannot be destroyed however it can be converted into some other forms . For example, rub your hands together quickly. You will feel them warm. You have used your muscular energy in rubbing hands as a result heat is produced. In the process of rubbing mechanical energy is converted into heat energy. Processes in nature are the results of energy changes. For examples, some of the heat from the sun is taken up by water in the oceans. This increases thermal energy. Thermal energy causes water to evaporate from the surface to form water vapors. These vapors rise up and form clouds. As they cool down, they form water drops and fall down as rain. Potential energy changes to kinetic energy as the rain falls . This rain water may reach a lake or a dam. As the rain water flows down, its kinetic energy changes into thermal energy while parts of kinetic energy of flowing water is used to wash away soil particles of rocks known as soil erosion. During the interconversion of energy from one form to other forms, the total energy at any time remains constant .

Question # 9

Define potential energy, explain its types

Ans 1: potential energy: the energy possessed by a body due to its position is called potential energy.
Examples:
- Stored water possesses the potential energy due to its height
- A hammer raised up to some height has the ability to do work because it possesses potential energy
Ans 2: Types:
- Elastic potential
- gravitational potential energy
Ans 3: Elastic potential energy; the energy present in a body due to the starched position is called elastic potential energy.
Example: a stretched bow has potential energy due to its stretched position
Ans 4: Gravitational potential energy: the energy present in a body due to its highest position is called gravitational potential energy.
Example: the energy possessed by a hammer due to its height
Ans 5: Explanation; let a body of mass m be raised up thorough height h from the ground. The body will acquire potential energy equal to the work done in lifting it to the height h.
Thus;
potential energy=P.E=F*h=w*h
P.E= mgh (here weight of body = w=mg)
Thus, the potential energy possessed by the body with respect to the ground is mgh and is equal to the work done in lifting it to height h.

Question # 10

Q no:6 (B) A 50 kg man moved 25 steps up in 20 seconds. Find his power , if each step is 16 cm high.

Ans 1: m= 50 kg
Height of h= 16 cm
each step = 0.16m
n= 25
t = 20s
p= ?
Since
F = w
= mg
= 50 x 10
= 500N
Height = h= 0.16 x 25 = 4m
reached by man
As we know that
P =w/t = F x s/t
By putting the values
P= 500 x y/20
= 2000/20
= 100w Ans

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Matric Part 1/9th Class Physics Chapter 6 Long Question With Answer for Unit 6 Work and Energy

9th Class English Medium Subjects

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Online Long Questions For Chapter 6 "9th Class Physics Chapter 6 Long Question Preparation "

Physics (New Book) - 9th Class Physics Chapter 6 Long Question Preparation

Q no:7 (B) Define Kinetic energy. Derive its formula K.E =1/2 mv²

What is meant by renewable sources of energy?

Write a note on energy a nd environment

What are nuclear fuels? explain it

What are fossil fuels? explain

Explain the mass-energy equation

What is energy converter ?

How is energy converted from one form to another? Give some examples

Define potential energy, explain its types

Q no:6 (B) A 50 kg man moved 25 steps up in 20 seconds. Find his power , if each step is 16 cm high.

Prepare Complete Set Wise Questions For Chapter 6 "9th Class Physics Chapter 6 Long Question Preparation "

Set 1

Set 2

9th Class Physics Chapter 6 Long Question Preparation - Set 1

Q no:7 (B) Define Kinetic energy. Derive its formula K.E =1/2 mv²

What is meant by renewable sources of energy?

Write a note on energy a nd environment

What are nuclear fuels? explain it

What are fossil fuels? explain

Explain the mass-energy equation

What is energy converter ?

How is energy converted from one form to another? Give some examples

Define potential energy, explain its types

Q no:6 (B) A 50 kg man moved 25 steps up in 20 seconds. Find his power , if each step is 16 cm high.

9th Class Physics Chapter 6 Long Question Preparation - Set 2

Write and explain energy conversion processes involved in producing of electricity

Define work. when a force do work? explain

Q no:6 (B) A 50 kg man moved 25 steps up in 20 seconds. Find his power , if each step is 16 cm high.

Write note on solar house heating and solar cells

What is efficiency? explain working of an ideal system.

What is energy converter ?

Define power and explain its units

Write a note on energy a nd environment

How is energy converted from one form to another? Give some examples

What is meant by renewable sources of energy?

9th class Physics Chapter 6 Long Q's (English Medium)

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